The present invention generally relates to radial inflow turbines and more particularly to nozzle configurations that mitigate resonant vibrations in turbine wheels.
Radial inflow turbines may be employed in applications that require varying output. For example, in an aircraft air cycle machine, it is desirable to control turbine output using a simple and efficient inflow system in which fixed-vane nozzles may be mounted directly onto a stator. The stator may divide inflow of gas into a high flow path and a low flow path. Each of the paths may be provided with a series of fixed nozzle vanes. By using either of the two paths separately or in combination, a desirable control of turbine output may be achieved.
As a wheel of the turbine rotates, its blades may interact with downstream edges of the vanes. At some turbine speeds, these blade to vane interactions may occur at an integer multiple of a natural frequency of the wheel, resulting in undesirable resonant vibrations of the wheel. It is possible to change a designed configuration of a wheel of a turbine to eliminate resonant vibrations if such vibrations are observed during initial trial runs of a new turbine design. However, such design reconfigurations are both costly and time-consuming.
As can be seen, there is a need to provide a radial inflow turbine in which resonant vibrations of a wheel are mitigated irrespectively of an initial design shape of the wheel and/or fixed nozzle vanes positioned on a stator of the turbine.